The configuration of human teeth requires that the ideal bristle contour for toothbrushes for brushing the buccal or outside surfaces of teeth be concave and that the ideal bristle contour for brushing the lingual or inside surfaces of teeth be convex. Most brushes have a single piece head which is of comparable thickness to the handle and which is relatively rigid and of a fixed curvature or configuration.
A further drawback of conventional brushes is that pressing the brush sufficiently hard against the teeth to get good cleaning risks damaging or discomforting the softer, adjacent gums. To a certain extent this can be solved by modifying the configuration of the brush, or by varying bristle hardness or length, though again, a single configuration cannot be optimum for all circumstances.
Some brushes may, however, incorporate a means for allowing the head to flex relative to the handle, as described for example in EP-A-371,293. Even so, such brushes have limited effectiveness. Other brushes are known which are adjustable into several different but fixed configurations. Adjustable toothbrushes are often difficult to manipulate and may be unreliable.
WO 92/17093 discloses a toothbrush having a handle and at one end thereof a bristle-bearing head, wherein the head is in the form of two or more segments flexibly and resiliently linked to each other and/or to the handle, one or more of the segments being bristle bearing. In one embodiment this is achieved by the use of transverse, and optionally longitudinal, grooves on the opposite face of the head to the bristles. The grooves can be wholly or partially filled with an elastomer.
Co-filed application WO 92/17092 further discloses a toothbrush having a handle and at one end thereof a bristle-bearing head which is flexibly and resiliently linked to an extended portion of the handle. The space between the head and the handle may be filled with an elastomer. The applicant markets a brush called the ‘Schwingkopf’ under the name ‘Dr. Best’ which contains some of the features disclosed in WO 92/17092. The brush has an elastomeric handle grip and an elastomer filled groove connecting the grip to an elastomer filled region in the neck of the brush. However, the brush does not contain transverse grooves in the head.
It is well-known to provide elastomeric grips in the handles of toothbrushes. It is also known from the above-mentioned PCT applications to provide transverse grooves containing elastomer into a brush head. To the present applicant's knowledge however, it has not been disclosed how both these objects can be achieved using a conventional single-point, injection moulding process.
It has now been found that all of the elastomer filled areas of the brush can be filled by a single-point injection moulding process by providing one or more elastomer supply channels which connect the grooves in the head to the grips in the handle.
It is accordingly an object of this invention to provide a toothbrush with a flexible head and handle grips which can be made by a simple injection moulding process.
It is yet a further object of this invention to provide a toothbrush which has good long-term durability.